In plumbing, pipe joints made of plastic material or the like are made using metal fittings onto which the pipes are inserted. The ends of the pipes are previously widened by means of socket pliers provided with an expansion tool.
After the socket is made, the pipe is immediately inserted onto the fitting and, due to the elastic properties of the plastic material, the pipe tends to resume its initial shape and fits tightly around the fitting, which is sufficient for their making integral, which is however completed by the presence of a widened external collar and at the same time as the end of the pipe.
A socket on a pipe made of plastic material is not made quite in the same way as a socket on a pipe made of annealed copper. One should indeed widen enough the end of the pipe in order to allow the insertion before the recovery of the shape, yet avoiding the creation of a plastic distortion instead of an elastic distortion.
Furthermore, for obvious reasons of strength, the thickness of the pipe wall increases with its diameter, and the more the thickness increases, the quicker the elastic return occurs, which requires a more considerable widening.
As well known, socket pliers, traditionally used for making sockets in pipes made of annealed copper, comprise, on the one hand, an expansion tool including a cylindrical end piece formed of the closure of several sector-shaped and radially mobile jaws and, on the other hand, a conical needle axially moveable by operating two arms, capable of being inserted between said jaws, in a conical recess, in order to cause them to spread apart, the restoring into the initial position occurring through elastic means. Advantageously, the tool is detachable from the pliers, which allows to adapt on the latter the tool corresponding to the diameter of the pipe to be widened and, therefore, to use the same pliers for several diameters.
It should be noted that the pliers can be operated manually or motorized through hydraulic means, for example.
These socket pliers have however limitations, in particular as regards pipes made of plastic material of a large diameter, for example in the range of 40 mm. In order to make a socket on such a pipe, which requires that the widening diameter exceeds the nominal diameter by about 50%, it is necessary to use a special technique as well as an expansion tool having specific features. It is indeed not possible to complete the widening in one single operation, on the one hand because of the force required, on the other hand due to the amplitude of the widening to be made and that, limited, of the displacement of the jaws, and, yet on the other hand, in order to avoid the creation of a plastic distortion.
Therefore, one proceeds to a succession of widening operations together with a progressive penetration of the end piece into the pipe. In order to implement this technique, the end piece has a slightly conical extreme portion that is aimed at being progressively inserted into the pipe.
Frequent cases of leaks have however been found on sanitation installations using pipes made of plastic material of a large diameter, said leaks being caused by sockets of an uneven shape.
Actually, during the first steps of the widening operation, only the end of the tool is acting and, because of the offset of the stress with respect to the action of the conical needle, the jaws bend and are positioned irregularly with respect to each other, thus creating local plastic distortions of the material, which are prejudicial to the elastic recovering and therefore to the tightness of the integral connection.
One could contemplate using specific tools associated to particular pliers, i.e. including a needle of more considerable dimensions, which however disadvantageously constrains the user to multiply the number of necessary pliers.
In order to try to cope with this disadvantage, an adapter device has been provided in FR 2,300,638, aimed at being mounted, as an intermediate part, onto pliers and at receiving an expansion tool. This adapter includes, internally, a member capable of being inserted between the conical needle and the jaws of the expansion tool, it includes for this purpose an end having a conical recess aimed at co-operating with the conical needle of the pliers and, at its other end, it has a conical shape aimed at co-operating with the conical recess of the jaws of the tool, the coning angles being identical, but the diameters being different.
It is therefore possible to choose the adapter device corresponding to the tool one wants to use. However, this device does not allow to fully solve the problem raised, in that, apart from the need for the user to have several adapters and, therefore, to have to transport them to the working site, said user has to regularly change the adapter according to the diameter of the pipe to be widened, being constrained to verify each time whether said adapter fits the tool to be used. In fact, this device corresponds to the above-mentioned solution, i.e. having to use several pliers.
It would be quite possible, in order to avoid using several adapters having different dimensional characteristics, to provide one single adapter having average dimensional characteristics, so that a large number of tools can be adapted thereto, which disadvantageously results into a work far from being optimal for the majority of diameters used.